Furnace flue damper



Aug. 5, 1,941.

' H. M. CUNNINGHAM FURNACE FLUE DAMPER Filed Nov. '7, '1939 INVENTOR ATTORNEYS.

Patented Aug. 5, 1941 UNITED STATES PATENT ()FFIC 2,251,440

FURNACE FLUE DAMPER Hal M. Cunningham, New Britain, Conn. application November 7, 1939, Serial No. 303,228

14 Claims.

This invention relates to dampers, and especially to flue dampers for furnaces either of the domestic or of commercial or industrial types.

One of the primary objects is to improve combustion by accurate control of draft, the damper of the present invention being fully automatic in its operation.

More specifically, it is an object of the invention to provide substantially uniform furnace draft, notwithstanding fluctuations in flue temperature and other variable factors,- such as wind direction and velocity, all of which usually have marked influence on furnace draft.

The nature, objects and advantages of the invention, as well as the operation of my improved damper, can be discussed to best advantage with reference to a typical domestic furnace installation adapted to the burning of oil.

In such oil burning installations, the oil is customarily fed in measured quantities by a pump, or equivalent means. Naturally, for efficient and perfect combustion of a given quantity of oil, an exact predetermined quantity of air is required.

With air supplied to the combustion chamber in whole or in part under the influence of chimney draft, the quanity of air admitted to the combustion chamber obviously varies in accordance with a number of factors,such as those mentioned above (for example, flue temperature) and in consequence, in installations of this type, in the absence of some control of the draft, imperfect and ineiiicient combustion takes place throughout most, if not all, of the time the furnace is in operation.

The problem in a domestic installation (and also in numerous commercial and industiral installations) is further complicated by the fact that, for economic reasons, the operation is ordinarily intermittent, resulting in repeated changes in flue temperature and other conditions throughout each day.

Numerous dampers have been proposed heretofore for this purpose but they have been found ineffective in control, irregular in operation, and

. inadequate to provide eflicient combustion. The

present invention provides a damper which is fully automatic and which maintains a very high degree of uniformity in ing conditions.

draft under widely Vary In general, the improved damper of the present invention comprises a gate adapted to be mounted in the aperture or opening in the flue running from the furnace to the chimney or stack, the gate serving to admit more or less airinto the fine, in accordance with increases and decreases in chimney draft, thereby maintaining uniform admission of air into the combustion chamber through the openings provided for that purpose.

The manner in which the objects and advantages' of the invention are carried out will be further apparent from the following description, referring to the accompanying drawing, in Which-- Figure l is a plan view of a portion of a flue pipe having an opening therein equipped with the improved damper of this invention, the damper being shown in section as indicated by the section line l-I on Figure 2;

Figure 2 is an enlarged inner elevational view of the damper;

Figure 3 is a Vertical sectional view taken as indicated by the line 3-3 on Figure 2;

Figures 4 and 5 are ilar to the showing of Figure 3 but illustrating the gate indifferent positions; and

Figure 6 is a view similar to Figure 3 but illustrating a modified arrangement.

I In Figure 1 the flue appears at l, the direction of gas flow therein being shown by the arrows, the portion a of the flue being extended to the combustion chamber and the portion b to the stack. The flue is apertured and provided with a transverse branch 8 adapted to reecive the damper. The damper includes a flanged frame 9 adapted to fit and cooperate with the mouth of the branch 8. The frame, and also the gate 10, are shown as being circular, although other shapes may be employed if desired.

The gate itself takes the form of a circular sheet metal plate which is desirably reinforced by an angle H positioned approximately diametrically thereof and also by angle members l2, I3 and 14-14.

Toward opposite ends of angle member H, a pair of pivot devices l5-l5 are secured to the gate and project in opposite directions beyond the edge of the gate to "cooperate with pivot bearings mounted within bearing straps 16-! E diagrammatic views sima pair of additional carried by the frame 9, and serving to pivotally mount the gate for movement to open and close mounted so that in closed position the inner face of the gate is subject to flue pressure or draft action, the outer face being exposed to atmosphere.

In contrast with most prior damper arrangements, the damper of the present invention is provided with a pivot axis which is located diametrically substantially at the center of the damper to provide gate areas at opposite sides which, when the gate is in closed position, are in substantial aerostatic balance. Thus, in the absence of some means upsetting this balance, the gate would not open under the influence of differential pressure asbetween the zones inside of and outside of the gate. For reasons brought out more fully hereinafter, I prefer to employ a gate having the aerostatic balance referred to, the action thereof being more accurate in various positions of the gate.

However, in order to provide for automatic opening of the gate upon a .predetermined increase in draft, the invention provides a means for upsetting the normal aerostatic balance when the gateis at or near closed position. This means includes an air chamber formed in part by baiile wall ll which is secured to theinner edge of the flange of frame 9 and which has an edge l8 bent toward the gate, as clearly appears in Figures 2 and 3. When the gate is in full closed position,

' therefore (see Figure 3) a chamber I9 is formed adjacent the inner face of an upper portion of the gate area. This chamber has relatively free communication with atmosphere through the parti-annular space between the edge of the gate and the frame 9, as indicated at 20 in Figure 3. The chamber, on the other hand, has relatively restricted communication with the interior of the flue. In consequence, the pressure in the chamber l9 and at the adjacent portion of the inner face of the gate remains closer to atmospheric pressure than does the pressure in the flue and adjacent the remainder of the inner face of the gate.

The above provision upsets the aerostatic balance of the gate, in consequenceof which, the lower edge thereof will be moved inwardly (for example, to the position shown in Figure 4) upon drop in flue pressure (increase in draft) to a predetermined value.

The foregoing pressure aerodynamic action of the air entering the flue and striking the lower half of the gate which is moving into the flue branch 8. Under this action the gate will move anywhere up to the full open position, depending upon the draft c0 idition, the

' opening movement being assisted by some aerostatic unbalance at opposite faces of that portion of the gate which swings into the flue opening.

The aerostatic and aerodynamic moments tending to open the gate may be opposed either by employing spring means urging the gate toward closed position or by weighting of the gate. If spring means be employed, they should preferably be arranged to provide approximately uniform closing force substantially throughout the entire range of movement of the gate.

In the embodiment illustrated, weighting is illustrated for effecting closing movement of the gate. For this purpose I prefer to employ a weight of the type indicated at 2|, constituting a knurled nut threaded on a screw 22 which, in

turn, is fastened to the gate by slightly spreadingdamper may be adjusted to give the desired draft notwithstanding varying conditions encountered in different installations. In all positions of adjustment, however, it will be noted that the weight is so located with reference to the pivotal Y axis and to the gate area that a closing force is provided under the influence of gravity throughcondition is maintained (at least in part) throughout a substantial portion of the opening movement from full closed position. The effectiveness of the chamber, however, decreases, especially after reaching the position of Figure 4, in which the free edge of angle member I2 is just about to leave its position of close proximity to the flange l8' forming the lower edge of the air chamber. The action of the air chamber substantially completely disappears about or a little -beyond the position of the gate shown in Figure 5, i. e., at a gate position of about 30-40.

Continued opening movement of the gate will now take place with further pressure reduction in the flue (further increase in'draft) under the out the entire range of gate movement between full closed and full open positions. The particular location of the weight is further of importance in maintaining the accuracy of draft control herein contemplated. Note, for example, that in full closed position the position of the weight is such that its effect is noticeably less than maximum, the maximum effect being secured when the weight projects horizontally as in Figure 5. In the range of gate movement in the neighborhood of Figures-4 to 5 (when the closing force of the weight reaches its maximum), the fln l2 which is desirably made of substantial width, aids in maintaining the action of the air chamber and thus in maintaining the opening force at a value sufficiently high to avoid any undesirably abrupt increase in draft in the furnace. As the gate approaches its full open position, the weight again loses some effectiveness, and with this in mind the upstanding portion of angle member I3 is so proportioned that the air entering the flue along the upper side of the gate strikes the angle member and contributes an additional aerodynamic moment tending to move the gate toward closed position.

A stop member 22a is arranged to cooperate with the screw 22 to limit opening movement or the gate.

From the foregoing it will be noted that the forces tending to open the gate are in part aerostatic and in part aerodynamic, the former pre dominating in full closed position and the latter predominating after the gate has moved substantially fromthe full closed position. By careful arrangement ofthe parts, as above outlined, and as illustrated, it will be found that an unusual degree of uniformity in draft may be secured in the combustion chamber, notwithstanding wide variations in-the flue. By way of illustration,

2,251,440 pressure readings were taken under various con-- ditions, showing the following results (all figures in hundredths of an inch of water pressure drop).

In one test the draft was increased in the chimney end (b) of the flue, as shown in Figure 1, throughout a range from 1 to 15 and then pressure drop readings were taken in the flue at end a,

showing the following results:

Test 1 (Gate set to hold draft at .045") Draft at a with Draft at :1 Variation gate held in with gate from desired closed position free value Inches Inches Inches 05 .0425 0025 l2 045 15 .045 .00

In another test, an even wider range of draft fluctuation was tested, giving the following readings:

Test 2 Fromthe foregoing it will be seen that even with wide fluctuations in the chimney draft, the

draft through the combustion chamber varies very little indeed from the desired value.

For purposes of comparison and information, one of the currently most widely used prior art dampers was given each of the two tests above under identical conditions, with the following results:

Test 1 (Gate set to hold draft at .045") Draft at a with Draft at a Variation gate held in with gate from desired closed position free value Inches Inches Inches .05 045 .00 .12 09 045 .15 .10 I .055

Test 2 (Gate set to hold draft at .035") Draft at a with Draft at a Variation gate held in with gate from desired closed position free value Inches Inches Inches 05 035 00 While I prefer the damper arrangement above described, certain features of the invention are also applicable to a damper having an off center pivot mounting, i. e., one in which the gate is not aerostatically balanced when in full closed position. A gate of this type appears inthe showing of Figure 6 as applied to a flue branch 8, the

damper including a frame 9a acting as a support for the gate 10a having an off center pivot 15a. In this arrangement an aerostatic unbalance normallf'serves to eflect opening movement of the gate, the closing movement being efl'ectedunder the influence of gravity. For the closing movement, either the unbalance in weight normally provided by offsetting the pivot may be relied upon, or the gate maybe equipped with'a supplemental weight or spring.

As shown in Figure 6, an air chamber is provided by a member 24 cooperating with the outer face of the gate at the side of the pivot 15a on which lies the larger gate area. The chamber has relatively free communication with the interior of the flue through a slot or aperture 25, so that in closed position, a portion of the outer face of the gate is subjected to'a pressure lower than atmospheric. This tends to resist the initial opening movement of the gate which is advantageous in the type of damper illustrated-in Figure 6, since one defect of that type is its tendency to commence opening movement too readily under the influence of even a small drop in flue pressure. the feature of my invention providing for use of an air chamber for transferring the pressure condition at one face of the gate to a portion of the other face thereof, may also be employed in a damper of the type illustrated in Figure 6 for the purpose of smoothing out the draft and thereby improving efliciencyand uniformity of combustion.

I claim:

1. A furnace flue damper including a gate having pivot means for mounting it in a flue opening for movement to'open and close the flue opening, the gate in closed position beingexposed to a zone of atmospheric pressure on its outer face and to a zone of flue pressure on its inner face, thepivotal axis being positioned to provide gate areas v at opposite sides of the axis in substantial aerostatic balance, means cooperating with the gate in closed position to form a chamber adjacent the inner face of the gate toward one side of the pivotal axis, which chamber, with the gate at or near closed position, has relatively free communication with the pressure zone adjacent the outer face of the gate but restricted communication with the pressure zone adjacent the inner face thereof, whereby to upset said aerostatic balance and provide for opening of the gate under the influence of a pressure drop in the flue, and means normally urging the gate toward closed position. i 2. A furnace flue damper including a gate having pivot means for mounting it in a flue opening for movement to open and close the flue opening, the gate in closed position being exposed to a zone of atmospheric pressure on its outer face and to a zone of flue pressure on its inner face, the pivotal axis being positioned to provide gate areas at opposite sides of the axis in substantial aerostatic balance and further to provide for movement of a portion of the gate into the flue opening and of another portion thereof out of the flue opening as the gate moves from closed toward open position so that the flow of air enter ing the flue after the gate has moved substantially from closed position acts aerodynamically on the gate to move the gate further toward open position, means cooperating with the gate in form a chamber adjacent the inner face of the gate toward one side of the pivotal axis, which chamber, with the gate at or near closed position, has relatively free communication with the pressure zone adjacent the opening, the gate in closed assassin the gate in closed position to form a chamber tion with the pressure zone adjacent the inner face thereof, whereby to upset said aefostatic balance and provide for opening of the gate under the influence of a pressure drop in the flue, and means normally tending to urge the gate toward closed position in opposition to the force tending to open the gate aerodynamically.

3. A furnace flue damper including a gate having pivot means for mounting it in a flue opening for movement to open and close the flue position being exposed to a zone of atmospheric pressure on its outer face and to a zone of flue pressure on its inner face, the pivotal axis being positioned to provide gate areas "at opposite sides of the axis in substantial aerostatic balance, and means cooperating with the gate in closed position to form a chamber adjacent the inner face of the gate toward one side of the pivotal axis thereof, which chamber, with the gate at or near closed position, has relatively free communication with the pressure zone adjacent the outer face of the gate but restricted communication with the pressure zone adjacent the inner face thereof, whereby to upset said aerostatic balance and provide for opening of the gate under, the influence of a pressure drop in the flue.

4. A furnace flue damper including a gate having pivot means for mounting it in a flue opening for movement to open and close the flue opening, the gate in closedposition being exposed to a zone of atmospheric pressure on its outer face and to a zone of flue pressure on its inner face, the pivotal axis being positioned to provide gate areas at opposite sides of the axis in substantial aerostatic balance and further to provide for movement of a portion of the gate into the flue opening and of another portion thereof out of the flue opening as the gate moves from closed toward open position so that the flow of air entering the flue after the gate has moved substantially from closed position acts aerodynamically on the gate to move the gate further toward open position, means cooperating with the gate in closed position to form a chamber adjacent the inner face of the gate toward one side adjacent the inner face of the gate toward one side of the pivotal axis thereof, which chamber, with the gate at or near closed position, has relativeiy free communication with the pressure zone adjacent the outer face of the gate but restricted communication with the pressure zone adjacent the inner face thereof whereby to upset said aerostatic balance and provide for opening of the gate under the influence of a pressure drop in the flue, the gate being weighted in a sense tending to move the gate about its pivotal axis from open toward closed position in opposition to the force tending to open the gate aerodynamically.

6. A furnace flue damper including a gate having pivot means for mounting it in a flue opening for movement to open and close the flue opening, the pivotal axis being positioned to provide gate areas at opposite sides of the axis in substantial aerostatic balance and further to provide for movement of a portion of the gate into the flue opening and of another portion thereof of the pivotal axis thereof, which chamber, with the gate at or near closed position, has relatively free communication with the pressure zone adjacent the outer face of the gate but restricted communication with the pressure zone adjacent the irmer face thereof, whereby to upset said aerostatic balance and provide for opening of the gate under the influence of a pressure drop in the flue, and means normally tending to urge the gate toward closed position in opposition to the force tending to open the gate aerodynamically.

5. A furnace flue damper including a gate having pivot means for mounting it in a flue opening for movement to open and close the flue opening, the gate in closed position being exposed to a zone of atmospheric pressure on its outer face and to a zone of flue pressure on its inner-face, the pivotal axis being positioned to provide gate areas at opposite sides of the axis in substantial aerostatic balance and further to provide for movement of a portion of the gate into the flue opening'and of another portion thereof out of the flue opening as the gate moves from closed toward open position so that the flow of a air entering the tide after the gate has moved substantially from closed position acts aerodynamically on the gate to move the gate further toward open position, and means cooperating with out of the flue opening as the gate moves from closed toward open position so that the flow of air entering the flue after the gate has moved substantially from closed position acts aerodynamically on the gate to move the gate further toward open position, and means operative at or near closed position for upsetting said substantial aerostatic balance to effect initial opening movement of the gate, and the gate being weighted to provide a closing force in opposition to the force tending to open the gate aerodynamically.

7. A furnace flue damper in accordance with claim 1, in which the means normally urging the gate toward closed position has a closing force which is different in different positions of the gate, being at a maximum at a point approxiclosed positions.

8. A furnace flue damper in accordance with claim 6, further characterized by the provision of a fin projecting from the inner face of the portion of the gate which moves into the flue upon opening movement, the fin being positioned at that side of the pivotal axis providing an aerodynamic moment tending to close the gate under the influence of airflow entering the flue opening.

9. A furnace flue damper in accordance with claim 6, further characterized by the provision of a fin projecting from the inner face of the portion of the gate which moves into the flue upon opening movement, the fin being positioned at that side of the pivotal axis providing an aerodynamic moment tending to close the gate under the influence of airflow entering the flue opening and further arranged so that the maximum aerodynamic moment tending to close the gate is secured adjacent the full open end of the range of movement of the gate.

10. A furnace flue damper including a frame adapted to be mounted in a flue opening, a gate pivotally mounted in said frame for movement to open and close theflue opening, the gate in closed position being exposed to a zone of atmospheric pressure on its outer face and to a zone of flue pressure on its inner face, the pivotal axis being positioned to provide gate areas at opposite sides of the axis insubstantial aerostatic balance and further to provide for movement of a portion of the gate into the flue opening and of another portion thereof out of the flue opening as the gate moves from closed toward open position so that the flow of air entering the flue after the gate has moved substantially from closed position acts aerodynamically on the gate to move the gate further toward open position. and means carried by said frame and forming an air chamber adjacent the inner face of the portion of the gate area which moves out of the flue during opening movement, said chamber, with the gate at or near closed position, having relatively free communication with the pressure zon adjacent the outer face of the gate but restricted communication with the pressure zone adjacent the inner face thereof, whereby to upset said aerostatic balance and provide for opening of the gate under the influence of a pressure drop in the flue.

11. A furnace flue damper including a gate having pivot means for mounting it in a flue opening for movement to open and close the flue opening, the gate in closed position being exposed to a zone of atmospheric pressure on its outer face and to a. zone of flue pressure onits inner face, the pivotal axis being positioned to provide gate areas at opposite sides of'the axis in substantial aerostatic balance andfurther to provide for movement of a portion of the gate into the flue opening and of another portion thereof out of the flue opening as the gate moves from closed toward open position so that the flow of air entering the flue after the gate has moved substantially from closed position acts aerodynamically on the gate to move the gate further toward open position, and means cooperating with the gate in closed position to form an air chamber adjacent the inner face of the portion of the gate area which moves out of the flue during opening movement, said chamber, with the gate at or near closed position, having relatively free communication with the pressure zone adjacent the outer face of the gate but restricted communication with the pressure zone adjacent the inner face thereof, whereby to upset said aerostatic balance and provide for opening of the gate under the influence of a pressure drop in the flue. .c

12. A furnace flue damper including a frame adapted to be mounted in a flue opening, a gate pivotally mounted in said frame for movement to open and close the flue opening, the gate in closed position being exposed to a zone of atmosbeing positioned to provide gate areas at opposite sides of the axis in substantial aerostatic balance and further to provide for movement of a portion of the gate into the flue opening and of another portion thereof out of the flue opening as the gate moves from closed toward open position so that the flow of air entering the flue after the gate has moved substantially from closed position acts aerodynamically on the gate to move the gate further toward open position and baiiie means associated with the frame and with the gate and cooperating to form a chamber adjacent one face of the gate toward one side of the pivotal axis, which chamber, throughout an initial portion of the opening movement has relatively free communication with the pressure zone adjacent the other face of the gate but restricted communication with the pressure zone adjacent said one face thereof, whereby to upset said aerostatic balance and provide for opening of the ate under the influence of flue.

.13. A furnace flue damper including a gate adapted to be pivotally mounted in a flue opening a for movement to open and close the flue opening,

the pivotal axis extending across the gate area in' a central region thereof. the gate in closed position being exposed to a zone of atmospheric pres-' sure on its outer face and to a zone of flue pressure on. its inner face andbeing movable toward open positionunder the influence of an increase of flue draft and toward closed position under the influence of a decrease in flue draft, and means forming a chamber adjacent one face of the gate when the latter is in closed position, which chamber, with the gate at or near closed position, has

relatively free communication with the pressure zone adjacent the opposite face of the gate but restricted communication with the pressure zone adiacent said one face. a

14. A furnace flue damper in accordance with claim 13, and in which the chamber is positioned at that side of the pivot axis providing for sub- Jection of a portion of the gate area to pressure in opposition to opening movement of the gate. HAL M. CUNNINGHAM.

a pressure drop in the g 

